Rotary cutting dies are used to cut and score sheets of corrugated board to produce a die cut product that can be manipulated into boxes. Rotary cutting dies typically include a curved die board that is configured to mount on a die cylinder. When used, the die cylinder and die board are mounted adjacent an anvil and a nip is defined between the cylinder and the anvil. Sheets of corrugated board are fed into and through the nip and, in the process, the sheet of corrugated board is cut and scored to form the die cut product. Die boards commonly include product and scrap cutting blades, scoring rules, trim and scrap strippers and product ejectors for separating the die cut product from the cutting die.
A common problem with rotary cutting dies that operate on corrugated board is that of controlling the pressure exerted against the corrugated board by the product ejectors. If the pressure is too great, the die cut product is damaged. That is, if the pressure is too great, the flutes are crushed. This makes the resulting boxes weaker and hence the boxes possess less stacking strength and the crushed flutes have a negative impact on the appearance of the product.
On the other hand, if the pressure exerted by the product ejectors is too low, then this will impact the separation of the die cut product from the cutting die during the die cutting operation. That is, if the pressure is insufficient to dislodge or remove the cut die product from the cutting die, it follows that the product will continue with the cutting die and the die cutting operation will be seriously impacted.
There have been attempts at controlling the pressure exerted by the product ejectors. For example, there have been attempts at using softer elastomer ejectors. This has met with only limited success. Even so, the softer elastomer product ejectors can be expensive and that alone has discouraged the adoption of some softer product ejector elastomers. Another attempt at solving this problem has been to use a water jet cutter to cut openings in the product ejectors. This has not proven completely successful. There are still problems with the pressure being too great and resulting in damage to the die cut product. In addition, the use of laser cut product ejectors adds significant cost to cutting dies.
There has been and continues to be a need for a rotary cutting die for cutting corrugated board that provides product ejectors that can exert sufficient pressure against the die cut product to separate the same from the cutting die but yet not so much pressure as to damage or crush the flutes of the die cut product.